1. Field
This disclosure is generally related to the field of solid state control systems and, more particularly, to the fault tolerant solid state control systems.
2. Description of the Related Art
Contactless switches are frequently used in control panel assemblies of vehicles such as airplanes. A control panel may include a plurality of switches that are in communication with a variety of electrical or hydraulic systems. In a typical system, actuation of the switch produces a relatively low current output to activate the switching action of a larger driver circuit. Such driver circuits are used to actuate a variety of systems, such as the landing gear or running lights of the vehicle.
Switches currently available for such systems include both contact and contactless switches. Contact switches include gold-plated leaf springs that may be actuated into and out of physical contact with the driver circuit. Typically, these switches include a tactile response to indicate when the switch changes state.
Contactless switches generally include a magnet and a sensor that is sensitive to magnetic forces to produce electronic control pulses. In a typical contactless switch, the magnets are permanently mounted to a device that is either rotated or linearly translated into close proximity with the sensors to change the state of the switch.
Contactless switches are well known. For example, U.S. Pat. No. 6,867,680 issued to Kulle discloses a contactless switch having a Hall effect sensor and dual magnets mounted on a magnet carrier. The magnets are arranged to have opposite magnetic poles facing the Hall effect sensor. When the switch is actuated, the magnet carrier and magnets mounted thereon are displaced relative to the Hall effect sensor. The positional displacement of the magnets relative to the Hall effect sensor alters the magnetic field detected by the Hall effect sensor. When the magnetic field detected by the Hall effect sensor reaches a predetermined level, the switch is actuated.
A problem with current contactless switches employing one or more Hall effect sensors is that the state of the contactless switch may change if one or more of the Hall effect sensors malfunctions.
Thus, there exists a need for a contactless switch that is not only tolerant of malfunctions, but is also economical to manufacture, has a high degree of reliability and meets the performance expectations of the end user.